Process of comminuting impure ddt



Patented Sept. 7, 1948 PROCESS OF COMMINUTING IMPURE DDT Isaac F. Walker, Hockeasin, DcL, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 18, 1940, Serial No. 042,122

This invention relates to insecticidal materials, and more particularly to an improved process for obtaining dispersible finely divided 1,1,1-trichloro-2,2-bis (p-chlorophenyl) ethane, hereinafter called DDT for convenience.

DDT is of great value as an insecticide in various military and civilian applications, One of the principal modes of applying DDT is by dispersing it as a solid material in finely divided form in inert liquid or solid diluents. DDT of high purity, i. e., having a setting point above 106 C., can be comminuted in high velocity gas disintegrators, e. g., in a "Micronizer, to the desired small particle size in high yields. However, when technical or partially purified grades of DDT, which contain substantial proportions of impurities, particularly 1,1,1-trichloro-2(p-chlorophenyl) -2-(o-chlorophenyl) ethane, are disintegrated in a Micronizer, a considerable amount of it, e. g., -15% or more, becomes packed into a solid cake or ring inside the grinding chamber. In addition to reducing the yield of DDT powder of the desired particle size, the solid cake or DUI reduces the 'pulverizing efliciency of the "Micronizer to such an extent that the pulverizing operation must be interrupted frequently to remove this cake of DDT from the grinding chamber. This packing oi impure DUI powder during Micronization is not substantially reduced by lining the inside of the grinding chamber with rubber or neoprene sheeting,

an expedient which is eilective in the Micronization of other crystalline organic compounds. Since DDT having a purity represented by material having a setting point of 102-106 C. is entirely satisfactory from the standpoint of its insecticidal properties, there exists a definite need for a process for reducing its particle size to the desired fineness in a high velocity gas disintegrator without losing excessive amounts of it by packing into a cake and without requiring frequent interruptions of the grinding to clean out p the pulverizing chamber to restore its operating efliciency.

It is an object of this invention to provide a new method for comminuting DDT in a high velocity gas disintegrator. Another object is to provide a method for comminuting impure DDT having a setting point between 102-106 C. which reduces the amount of DDT powder which packs into a cake in the pulverizing chamber of the high velocity gas disintegrator. Other objects will appear hereinafter.v

These objects are accomplished by the present invention or comminuting in a high velocity gas 8 Claims. (CL 187-40) charge.

. 2 disintegrator impure DDT having a setting point of 102-106 C. in the presence of a salt of an acid having an ionization constant of at least 3x10 at 25 C.

The invention is carried out by uniformly blending DUI having a setting point of 102-l06 c. with an aqueous solution of a salt of an acid having an ionization constant oi. at least 3X10-" at 25 (3., removing the water from the resulting paste, drying the coated DUI particles, and passing the dry DUI through a high velocity as disintegrator such as that known commercially as a Micronizer.

In a preferred embodiment of the invention the DUI is coated with a salt of an acid having an ionization constant of at least 3X 10- which is also capable of promoting dispersibility of wettability of the comminuted DUI.

The invention is illustrated by the iollowlng examples in which the proportions of the ingredients are expressed in parts by weight.

Example I A mixture 01' 820 parts of DDT having a setting point oi 103.5 0., 4.1 parts oi sodium dodecyl sulfate, and 600 parts of water is blended uniformly into a smooth paste, which is then placed in a tray over which a current 01' air at 50 C. is

circulated, After all the water is removed by.

evaporation, the resulting dry material is passed through an air "Micronizer." Only 1 part (0.12% of the weight of the total charge) oi DDT becomes packed into a cake in the circular grinding chamber of the Micronizer." This amount of caking does not reduce the operating efliciency of the Micronizer." A sample 01' the same DUI "Micronized without any anti-static agent forms a circular cake amounting to 15.6% of the total This amount of caking prevents satisfactory comminution oi the DUI, and the Micronizer must be shut down and cleaned out before satisfactory grinding can be continued.

Example II Example 111 A mixture of 820 parts of the DDT of Example II, 8.2 parts of lauryi pyridinium chloride, and 620 parts of water is blended together, after which the water is removed as in Example I. The dry material is passed through an air Micronizer." Twenty-eight parts (3.4% of the weight of the total charge) of DDT packs into a solid ring inside the Micronizer."

Example IV A mixture of 820 parts of DDT of the type of Example I, 4.1 parts of sodium dibutylphenylphenoldisulfonate (the material known commercially as "Aresklene 400") and 600 parts of water is blended together, after which the water is removed as in Example I. The dry material is passed through an air Micronizer." Only 13 parts (1.6% of the weight of the total change) of DDT packs into a ring inside the "Micronizer.

Example V A mixture of 810 parts of the DDT of Example I, 4.05 parts of tallow-coconut oil soap, and 600 parts of water is blended together and then the water removed as in Example I, after which the dry material is passed through an air "Micronizer." Seventy-five (75) parts (9.3% of the weight of the total charge) of the DDT packs into a ring inside the Micronizer.

Example VI A mixture of 810 parts of the DDT of Example I, 4.05 parts of sodium chloride, and 600 parts of water is blended together and then the water removed as in Example I. Twenty-one parts (2.6% of the weight of the total charge) of DDT packs into a ring when the dry material is passed through an air Micronizer.

The invention has been illustrated with particular reference to the Micronization of impure DDT in the presence of certain proportions of several specific salts and in a certain type of gas disintegrator; however, it is not limited to these specific embodiments. Other salts of acids having an ionization constant of at least 3x10 at C. are also suitable for use in the comminution of impure DDT in high velocity gas disintegrators. Examples of other salts of this type which can be used include: potassium acetate, ammonium sulfate, magnesium chloride, trisodium phosphate, sodium benzene sulfonate, sodium petroleum sulfonate, sodium ethyl sulfate, potassium carbonate, trimethylamine hydrochloride, etc. These salts are believed to act as antistatic agents in preventing excessive packing of the DDT powder in the pulverizing chamber of the disintegrator. Salts of the stronger acids, e. g., salts of hydrochloric, sulfuric and sulfonic acids, are preferred since they are the most effective, Salts of acids having ionization constants less than 3X10 .at 25 C., e. g., sodium silicate, and un ionized materials such as sucrose are not effective in reducing packing of DDT in a Micronizer.

Various proportions of these anti-static coatings canbe used in the practice of this invention. The examples have illustrated the use of /2% and 1% (based on the weight of the DDT) of certain salts. Larger or smaller proportions, for

example from 0.12 to 2%, however may be used if desired. Proportions of 1% and higher, however, are less effective than /'z% of the same antistatic agent. Thus, when 1% and 2% of sodium chloride are substituted for the /z% of that salt 4 used in Example VI with DDT of the same purity as in that example. 6.2 and. 11.0%, respectively,

of the total charge 01' DDT passed through the Micronizer" packs into a ring. Comparison of the results obtained in Examples II and III also shows the smaller amount of packing occurring when the lower percentages of the anti-static agent are used.

A separate dispersing agent such as for example, polyvinyl alcohol, methyicellulose, or the sodium salt of the oleic acid amide of N-methyi taurine known commercially as Igepon T, may optionally be added to the dry mixture of DDT and anti-static agent to promote the dispersibility of the finely divided DDT. It is preferred, however, to use as the anti-static coating a salt of the above-defined type which is also capable of promoting dispersibility or wettability, e. g., salts such as sodium dodecyl sulfate, sodium petroleum sulfonate, lauryl pyridinium chloride and sodium dibutylphenylphenoldisulfonate.

The amount of water used in blending the anti-static agent with the DDT is not critical. An amount at least suflicient to produce uniform coating of the salt on the DDT particles should be used. Quantities of water amounting to 60-100% of the DDT give satisfactory results but larger or smaller quantities may be used if desired. The use of larger amounts of water. will. of course, require the removal of larger amounts in the drying step, which would obviously be less economical.

This invention is of particular value in the manufacture of finely divided dispersible DDT powders since the present process provides a simple method for comminuting in a high velocity gas disintegrator such as a Micronizer" an impure grade of DDT, which is insecticidally active, without causing frequent interruption of the grinding operation to clean out the pulverizing chamber to restore its operating efliciency.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof. it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process which comprises comminuting in a high velocity gas disintegrator impure 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane having I a setting point of from 102 to 106 C. in the presence of a salt of an acid having an ionization constant of at least 3 X 10- at 25 C.

2. A process which comprises uniformly blending to a paste impure 1,1,1-trichloro-2,2-bis(pchlorophenyDethane having a setting point of from 102 to 106 C. and an aqueous solution of a salt of an acid having an ionization constant of at least .3 10" at 25 0., removing the water from the paste and drying the particles of 1,1,1-trichloro 2.2 bis(p-chlorophenyl)ethane coated with said salt, and passing the dried product through a high velocity gas disintegrator.

3. The process set forth in claim 1 in which the salt defined therein'is a wetting agent.

4, The process set forth in claim 1 in which the salt defined therein is a dispersing agent.

5. The process set forth in claim 1 in which said salt is a hydrochloric acid salt.

8. The process set forth in claim 1 in which 8 8. The process set forth in claim 1 in which said salt is sodium dibutylphenyiphenoldisulfonate.

ISAAC F, WALKER.

REFERENCES crrEn The following references are of record in the file of this patent:

UNITED STATES PATENTS 

